Molecular identity and location of invariant antigens on Trypanosoma brucei rhodesiense defined with monoclonal antibodies reactive with sera from trypanosomiasis patients.

Monoclonal antibodies (MAbs) which are reactive with several antigenically distinct variable antigen types were prepared by immunization with Trypanosoma brucei rhodesiense. Certain MAbs were shown to be specific for members of the genus Trypanosoma and not reactive with Leishmania spp. or Plasmodium falciparum by the indirect immunofluorescence assay. These genus-specific MAbs were used to identify the molecular location of these invariant antigen determinants in whole T. brucei rhodesiense antigen preparations. Two monoclonals reacted with a low-molecular-weight doublet of approximately 22,000 relative molecular weight on Western blots of whole trypanosome antigen preparations separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. These determinants did not appear to be on the variable surface glycoprotein molecule and were destroyed by trypsin digestion. Binding studies in which live, DEAE-purified, bloodstream trypanosomes were exposed to invariant antigen-specific MAbs suggested these determinants were accessible on living trypanosomes. Genus-specific MAbs also reacted with determinants present in sera from African trypanosomiasis patients in a dot immunobinding assay but not sera from patients with malaria or leishmaniasis. These results suggest that certain invariant molecules of African trypanosomes are immunogenic, possibly accessible on the trypanosome surface, and may be present as circulating invariant antigen in trypanosomiasis patients.